Method of making prestressed concrete beams



Feb. 1, 1966 WENNSTRGM METHOD OF MAKING PRES'I'RESSED CONCRETE BEAMSFiled Dec. 2'7. 1961 United States Patent 3,233,027 METHOD 0F MAKINGPRESTRESSED CONCRETE BEAMS Elof Wennstriirn, Femkampsgatan 25, Orebro,Sweden Filed Dec. 27, 1961, Ser. No. 162,542 2 Claims. (Cl. 264228) Thisinvention relates to a process for using a device for making prestressedconcrete beams and is essentially characterized by the fact that thedevice is a combination of a mould and means introduceable into saidmould for putting the reinforcing rods under stress, said stressingmeans being adapted for removal from the mould together with theconcrete beam cast in the mould and having the stressed reinforcing rodsembedded therein.

The invention is also concerned with a method of making prestressedconcrete beams with the use of the device according to the invention.This method is essentially characterized by the fact that the stressingmeans is removed from the mould together with the concrete beam cast inthe mould and having the stressed reinforcing rods embedded therein,before the beam has set so that the final setting of the concrete aroundthe reinforcing rods takes place outside the mould.

The invention makes it possible to make prestressed concrete beams inordinary moulds substantially at the same rate as customary reinforcedconcrete beams. As the device for making the prestressed concrete beamsmoreover is not very expensive, the invention permits manufacturingprestressed concrete beams at considerably lower costs than has hithertobeen possible.

For a better understanding the invention will be more fully described inthe following, reference being made to the accompanying drawing whichillustrates the method using an embodiment, chosen by way of example, ofthe device suggested by the invention. In the drawing:

FIG. 1 is a cross section of the device on line II in FIG. 2 before themould has been filled with concrete;

FIG. 2 is a top plan view of the device shown in FIG. 1;

FIG. 3 is a cross section on line IIIIII in FIG. 4;

FIG. 4 is a top plan view of a concrete beam immediately after it hasbeen removed from the mould;

FIGS. 5 and 6 are respectively an end view and a plan view of a concretebeam some time after it has been removed from the mould.

1 denotes the upwardly open mould in which the prestressed concrete beam2 is cast. According to the embodiment shown the concrete beam 2 is ofU-shaped cross section but it is understood that other cross sectionalforms can also be chosen.

According to the invention, the mould 1 is combined with means 3introduceable thereinto for stressing the reinforcing rods 4, and saidstressing means 3 is adapted for removal from the mould 1 together withthe concrete beam 2 cast in the mould 1 and having the stressedreinforcing rods 4 embedded therein.

As will appear from the drawing which shows a preferred embodiment ofthe stressing means 3, said means comprises two end wall members 5 and 6for the concrete beam 2, which members are constituents parts of themould 1, and a telescoping stressing element 7 arranged between said endwall members 5 and 6 which are provided with, or formed as, fasteningsfor the reinforcing rods 4.

In the position of the stressing means 3 introduced into the mould 1,the stressing element 7 is arranged to lie outside that part of themould 1 in which the con-crete beam 2 is cast. As shown in the drawing,the stressing element 7 thus lies beneath the bottom 8 of the mould 1,which bottom has a recess for accommodating the stress- Patented Feb. 1,1966 ing element 7. During casting a plate or like member is to coversaid recess in the mould bottom 8.

The stressing element 7 is removably secured to the end wall members 5and 6 in a per se known manner. The ends of the stressing element 7 canbe arranged to engage either the facing sides of the end wall members 5and 6, as is shown in the drawing, or the sides of said members 5 and 6which face away from each other.

After the reinforcing rods 4 have been secured to the end wall members 5and 6 with the aid of nuts 9, keys or like means the end wall membersare moved apart by means of any suitable device so that the reinforcingrods 4 are given the desired prestress. Then the two parts of thestressing element 7 are fixed relative to each other in a suitablemanner so that the prestress is maintained. The end wall members 5 and 6can be moved apart before the stressing means 3 is introduced into themould 1, but as will be seen from the drawing where the position of theend wall member 6 before prestressing is indicated by dash lines, theend wall members 5 and 6 can be moved apart also with the stressingmeans in position in the mould.

According to the preferred embodiment shown the mould 1 is pivotallymounted in a frame 10. Associated with the mould 1 is a cover 11 whichcan be secured thereto. After the mould 1 with the stressing means 3therein has been filled with concrete and possibly also vibrated thecover 11 is mounted in position on the mould which is then swung aboutthe shaft 12 to the position in which the opening of the mould 1 isturned downwards. The cover 11 is now caused to engage a base whereuponit is loosened from the mould 1. By displacing the mould 1 and the cover11 relative to each other the beam 2 with the stressed reinforcing rods4 therein and the stressing means 3 will leave the mould 1 and bedeposited on the cover 11, as will be seen from FIGS. 3 and 4. The beam2 can be deposited on the cover 11 practically immediately after castingand thus long before the concrete finally sets around the reinforcingrods 4. As a consequence, the mould 1 is immediately available forcasting a new beam with the use of another stressing means 3, since theearlier stressing means 3 still fulfills its function on the beam justeast. A given time after the concrete beam 2 has been removed from themould 1 but before the final setting of the concrete takes place, thestressing element 7 can be removed from the end wall members 5 and 6 andused in the casting of another prestressed concrete beam. This removalof the stressing element 7 is possible because the concrete beam 2 isnow capable, during the final setting of the concrete, of maintainingthe end wall members 5 and 6 at the distance determined for theprestressing. FIGS. 5 and 6 are meant to illustrate this. The time afterwhich the stressing element 7 is removed has to be determined from caseto case.

In the embodiment illustrated it is only the four reinforcing rods 4located in the web of the beam 2 that are put under prestress. However,in other embodiments all or other reinforcing rods 4 can be put underprestress.

During casting the suction between the concrete and the convergingoutwardly facing sides 13 of the mould 1 shall thus give thecorresponding sides of the concrete beam 2 rough surfaces to facilitatejoining of the concrete beams 2.

The above embodiment of the invention was described for purpose ofillustration rather than limitation. All conceivable variations ormodifications of the invention are understood as being included in thescope of the appended claims.

- tending between said end wall members, placing said end wall membersand reinforcing rods under stress by a stressing element removablyattached to said end Wall members, inverting said mold prior to finalsetting of said concrete and removing the mold but not said end wallmembers from the concrete beam formed, then removing said stressingelement from said end Wall members and allowing the concrete to finallyset.

2. A method as set forth in claim 1 wherein said stressing elements areremoved from said end Wall members after said concrete beam has beenremoved from the mold with said end wall members but before the finalsetting of the concrete.

UNITED STATES PATENTS 1,624,191 4/1927 Venzie 25118 2,080,074 5/ 1937Freyssinet et al. 25118 2,496,850 2/ 1950 Bertrand 25-418 XR 2,725,61212/1955 Lipske 25118 2,913,798 11/1959 Breguet 25118 2,966,717 1/1961Fuller et al. 25-118 XR FOREIGN PATENTS 61,275 11/1954 France. 974,18110/ 1960 Germany. 854,448 11/ 1960 Great Britain.

15 ALEXANDER H. BRODMERKEL, Primary Examiner.

ROBERT F. WHITE, Examiner.

1. A METHOD FOR MAKING PRESTRESSED CONCRETE BEAMS COMPRISING POURINGCONCRETE INTO A MOLD HAVING END WALL MEMBERS LOCATED IN SAID MOLD WITHREINFORCING RODS EXTENDING BETWEEN SAID END WALL MEMBERS, PLACING SAIDEND WALL MEMBERS AND REINFORCING RODS UNDER STRESS BY A STRESSINGELEMENT REMOVABLY ATTACHED TO SAID END WALL MEMBERS, INVERTING SAID MOLDPRIOR TO FINAL SETTING OF SAID CONCRETE AND REMOVING THE MOLD BUT NOTSAID END WALL MEMBERS FROM THE CONCRETE BEAM FORMED, THEN REMOVING SAIDSTRESSING ELEMENT FORM SAID END WALL MEMBERS AND ALLOWING THE CONCRETETO FINALLY SET.